First test of seismic invisibility cloak

February 7, 2013

Seismic metamaterial test (credit: Stéphane Brûlé et al.)

Engineers and physicists are developing acoustic versions of metamaterials that steer sound, which could be used to steer seismic waves around high-value buildings such as nuclear power stations or airports.

The Institut Fresnel in Marseille and the ground improvement specialist company, Menard, both in France, say they’ve built and tested a seismic invisibility cloak in an alluvial basin in southern France, MIT Technology Review reports.

The secret of invisibility cloaks lies in engineering a material on a scale smaller than the wavelength of the waves it needs to manipulate.  The appropriate sub-wavelength structures can then be arranged in a way that steers waves.

The French team created its metamaterial by drilling three lines of  empty boreholes 5 metets deep in a basin of silted clay up to 200 meters deep.

The experiment consisted of creating waves with a frequency of 50 Hertz and a horizontal displacement of 14 mm from a source on one side of the array. They then measured the way the waves propagated across it.

The French team says its metamaterial strongly reflected the seismic waves, which barely penetrated beyond the second line of boreholes.